Ductility and Hardening of Neutron-Irradiated Fe-Cr and Fe-Cr-Ni Steels

Fe-Cr and Fe-Ni-Cr steels are candidate alloys for fusion reactor materials. For future design it is important to clarify the general rules of mechanical properties for those alloys irradiated at higher fluence and at higher temperatures. In this investigation, to find general rules for irradiation effects, twelve kinds of commercial Fe-Cr and Fe-Ni-Cr steels were irradiated in JMTR. The total flux was 6 × 1025n/m2, and the irradiation temperature was 743 to 848 K. Yield strength, tensile strength, and uniform ductility at room temperature were observed for all specimens before and after irradiation, and work-hardening exponents were obtained from stress-strain curves of those specimens. In all cases, uniform ductility was equal to the work-hardening exponent, there was a close relationship between strength and uniform ductility, and there was no anomalous behavior in these alloy series. Further study was made of Fe-9Cr-2Mo steel, which was irradiated to 3 × 1026 n/m2 at 673 to 923 K in EBR-II. Electron micrographs for controlled or irradiated specimens were used for the analysis of the change of strength by irradiation. The strength and uniform ductility was interpreted from microstructural aspects.